Both of my main bikes have dropper seatposts, so I’d prefer not to clamp on that. And the fatbike has a double parallel toptube, so I can’t clamp to that. The full suspension bike has all of the cables routed along the toptube, so I can’t clamp there either. 😕
So I use a Thule Frame Adapter Its not perfect, as the bike can move around a bit if you really need to use a lot of force on something. But its not a problem for 99% of normal stuff.